This is a longitudinal study of growth and development of children at high or low risk of obesity. A cohort of 78 chilren of 2-3 years of age, selected on the basis of maternal body weight -- obese or lean, and already intensively studied, will be studied for a further two years. The goal of the study is to detemine risk factors for the development of human obesity. Members of the cohort were assessed at 3 months of age for body size and composition by measurement of length and weight, skinfold thickness, total body electrical conductivity (TOBEC) and isotope (2H and 180) dilution, energy expenditure (TEE) and indirect calorimetry for sleeping metabolic rate (SEE). Energy intake was assessed by measurement of sucking behavior and food intake. After two years of study there is no difference between high and low risk infants in body composition and most of the other measurements, meaning that the proposed study is truly prospective, before the onset of obesity/adiposity. The prospective study is designed to assess the influence on body composition at 3, 4, and 5 years of age of the putative risk factors that were measured at 3 and 24 months of age, and will be measured again at 4 years of age - TEE, SEE, TOBEC, DEXA, food intake and (at 3 months ) sucking behavior. In addition, we plan to measure psychosocial variables that have been propsed as risk for obesity and to move from maternal obesity as a selection factor to maternal and paternal body mass index (BMI=k/m2) as risk factors. Linear structural equation modeling will be used to assess the influence of the putative risk factors, singly and interactively, on body composition and adiposity. Finally we plan to bank lymphocytes of the parents and infants for future molecular genetic studies.